Telephone instrument



June s, 1928. 1,672,351

A. A. THOMAS TELEPHONE INSTRUMENT Filed Oct. 28, 1925 2 Sheets-Sheet 1 June 5, 1928. 1,672,351

A. A. THOMAS TELEPHONE INSTRUMENT Filed Oct. 28, 1925 2 Sheets-Sheet 2 XNVENTOR Patented June 5, 1928.

UNITED STATES PATENT oFFicE. f

.A DOLPH A. THOMAS, OF NEW YORK, N. Y.

TELEPHONE INSTRUMENT.

Application filed October as, 1925. Serial No. 65,282.

My invention is for a new and improved telephone instrument equally well adapted for use as transmitter and receiver. The

object of my invention is to provide an in strument of high efliciency and yet exceedingly simple construction. As will appear later, the instrument of my invention is particularly useful for radio broadcasting and reception, although not limited to that field.

One of the main features of my invention comprises anedge-free diaphragm of conducting material resiliently mounted-to vibrate in a magnetic field and adapted, to be connected in a suitable circuit, either to genminum and aluminum alloys, which havev the additional advantage of lightness. The supporting extensions of the diaphragm are preferably corrugated transversely to provide therequired resiliency. 1 In a preferred embodiment of my invention, the vibratory acoustic unit is supported on and between a pair of spring arms which are adjustableto regulate the normal tension or resiliency of the vibratory unit. This adjustment may be made from outside the casin of the instrument.

Various other-features and advantages of my new telephone instrument will become apparent from a detailed description of suitable einbodiments shown in the accompanying drawings, in which-- A for adjusting the normal resiliency ofthe -vibratory unit from outside the casing;

Fig. 4 is a vertical cross-section on line 44 of Fig. 5, showing a telephone transmitter embodying my invention;

Fig. is a face view of the construction shown, in Fig. 4, with the front plate or cover removed;

F ig. 6 is a transverse cross-section on line 6-6 of Fig. 5;

Fig. 7 is a fragmentary detailed view to show a form of readily separable connection between the end covers and the body of the casing in Figs. 4, 5 and 6;

-Fig. 8 is a fragmentary view, partly in section, showing the automatically adjust able connection between the spring frame which supports the vibratory, unit and the manually operated rod for adjusting the spring arms; and- Fig. 9 is a diagrammatic view of a modification in which the edge-free diaphragm is resiliently supported by coil springs.

Referring first to Figs. 1 and 2, the various parts of the operative mechanism 'are enclosed within an outer casing indicated as a whole by C. This casing, which may be made of non-magnetic sheet metal .ormolded of suitable composition material, consists of a cylindrical body section 1, a topor cover 2 and a laterally extended base 3. The cover 2 is referably secured to the 1 casing by a readiy separable connection, such as screw-threads 4 or otherwise. A hollow tubular extension 5 projects centrally from the cover 2 for receiving a horn' 6 or other suitable amplifier. ,A horizontal annular flange 7 extends laterally from the lower end of the body section 1 and forms with the base 3 a horizontal circular recess '8 in which is mounted a supporting disk 9 of suitable non-magnetic or insulating material. 'This disk fits snugly at its periphery against the right-angled shoulder formed by the lateral flange 7 and the upper portion of the base section 3, and is held in place by suitable fastening devices 9, such as removable screws or bolts. e

On the base-plate or disk 9 is mounted a magnet M, which is preferablyof the permanenttype. As shown in the particular embodiment illustrated, this magnet is bent sub-' stantially U-shaped and ponsists of a base 10, a pair of upright sides ll'and a pair of inwardly projecting pole pieces 12, one of which is marked the north ole (N) and the other the south pole (S). (gne or more bolts 13, or other suitable fastening. means, hold the magnet M securely in place on the base 9.

As seen in Fig. 2, the pole-pieces 12 of the magnet are separated by an air gap 14, and

in this air gap is operatively mounted a diaphragm 15. In the present instance, the diaphragm 15 is provided at opposite ends with a pair of integral extensions 16, which are transversely corrugated as indicated at 17. The diaphragm is a rigid plate or disk of suflicient area to operate efficiently for transmitting and receiving sound Waves. When I refer to the diaphragm as a plate or disk, I do not limit myself to any specific configuration, but I 'use the terms in the broadest possible sense. The .parts 15 and 16 constitutean acoustic vibratory unit, which may conveniently be stamped or out from a single piece of non-magnetic sheet metal having sufficient resiliency. The metal aluminum and some of its alloys will answer this purpose very well, but I want it understood that any suitable metal may be used for the vibratory unit.

The outer ends of the corrugated extensions 16 are attached to a pair of spring arms 18, which extend upwardly from a cross-piece 19. The members 18 and 19 are preferably shaped from a single strip of resilient material and thus constitute a single supporting frame for the vibratory unit. Screws 20, or other fastening devices, secure the supporting frame rigidly in position on the disk 9. Since the supporting member 18-19 is arranged at right angles to the magnet, the latter does not interfere with the mounting of the frame within a casing having a diameter only slightly greater than the length of the magnet. As the vibratory unit 15-16 is connected in circuit, the exten' sions 16 should be insulated from the me tallic supporting arms 18. This may be accomplished in any suitable way. In Fig. 1, I have shown the ends of the extensions 16 rigidly clamped to the arms 18 by insulated bolts 21, by which I mean bolts encased in or surrounded'by a sleeve of insulated material. An insulated washer 22 is interposed between the extensions 16 and the inwardly extending flanges 18 of the spring arms 18.

If desired, clampin plates 23 may be inserted between the bdlts 21 and the extensions 16 to insure a rigid connection for the vibratory unit. Theplates 23 may be of metal or hard insulating material.

In order to adjust the supporting arms 18 toward and from each other for the purpose of varying the normal tension or resiliency of the extensions 16, I provide a two-part rod 24 having screw-threaded ends 25 arranged toengage in a screw-threaded cylindrical finger piece 26. The screw-threads 25 run in opposite directions, so that when the finger piece 26 is turned in one direction, the rod sections 24-are separated, and when the finger piece is turned the other way, the rod sections are drawn together. The outer ends of the rod 24 are provided with c lindrical or transversely'elongated hubs 2 These hubs or hearing pieces are held in correspondingly shaped recesses formed by lateral bends 28 in the supporting arms 18. Retaining plates 29 are secured to the arms 18 by screws 20, or otherwise, for holding the hearing hubs 27 in firm contact with the arms 18 during the axial movements of therod 24.

.It is clear from Fig. 1 that, when the two sections of the rod- 24 are forced apart by turning the knurled finger piece 26, the

resilient arms 18 are likewise spread apart ends of the rod 24 is to compensate for the rocking movements of the arms 18 while the rod 24 moves in a straight line. The retaining plates 29 are provided with openings 29' which are slightly larger than the diameter of rod 24, so as to allow rocking movement of the arms 18 without binding the rod 24. The bearing pieces 27 are .preferably elongated transversely of the arms 18, in order to prevent rotation of the rod 24 when the same is adjusted by the rotary finger piece 26. If the bearing hubs.27 are made spherical, as they might be, it will be necessary to clamp them so firmly in place by means of the retaining plates 29 that rotation of the rod 24 will not take place during the axial adjustment thereof.

For conveniently connecting the vibratory unit 1516 in circuit, the ends of the extensions 16 maybe prolonged beyond the spring arms 18, as indicated at 16, and tothese projecting ends are secured conductors 30 and 31, which are led through a' hole 32 in the base 9 to a pair of binding posts or terminals 33 and, 34 secured to the underside of disk 9 within the base section 3 of the outer casing. The terminals 33 and 34 are adapted to receive a pair of circuit leads 35, which .pass

through an insulated hole 36 inthe base 3.

stood without' urther explanation, I need only sayf'that, as variable currents pass through the telephone circuit in which the vibratory conducting unit 1'5 16 is connected, the diaphragm 15 will vibrate transverse-' ly in the air gap 14 between the magnetic pole pieces, and these vibrations will correopening inthe cover 2, the vibrations of' '15 will reproduce the sound waves which originally caused the currentwariations in the telephone receiving circuit. Since the diaphragm isopposite and close to the sound the diaphragm will set in motion the column of air in the sound amplifier 6, so that the acoustic reproduction will be amplified sufli-' ciently to be heard at a distance. As the diaphragm is freeor unbound at the edge,

it has no fundamental note of its own and responds instantly and with equal fidelity to all vibrations occurring within the range of ordinary speech or music. Also, the vibratory unit 1516 can be made exceedingly light and its inertia is thus reduced to a minimum. Indeed, it is possible to make this vibratory acoustic unit so small and so light that for practical purposes its inertia'be- 'comes negligible. This obviously adds to the sensitiveness and efficiency of the instrument. Owing to the wa in which the diaphragm 15 is supported fiy the resilient extensions 16, it is free or floating at the edge and therefore vibrates with substantially equal amplitude over its entire area. I have attempted to indicate this in a crude way by the dotted lines 15 in Fig. 1. In the practical operation of the instrument, the amplitude of vibration of the diaphragm 15,'even at its maximum, will be but a very small fraction of" an inch, and so the pole pieces 12 need not be very thick.

- The volume of the reproduction, and to some extent also its quality, is controlled by regulating the normal tension of the vibra tory unit, as previously described. For instance, by spreading the arms 18 and thus increasing the tension of the extensions 16, the normal load (if I may call it that) on the diaphragm 15 is correspondingly increased, and the diaphragm will not vibrate as freely or with the same amplitude (ceteris paribus) as when the tension on the member 16 is relaxed by bringing the arms 18 closer together. The finger piece 26, therefore, regulates the degree of loudness of the reproduction. It goes without saying that theresilien'cy of the extensions 16 should be such that the diaphragm 15 instantly responds without lag or sluggishness to variations in ficient area for proper reproduction and is otherwise of such suitable shape that the flux across the air gap produces the required -magnetic field for the diaphragm. In Fig.-

2., the pole pieces 12 are shaped to produce an air gap which is slightly narrower at the ends than at the middle, in order to provide a more uniform distribution of the flux across the air gap by reducing the reluctance across the ends thereof The diaphragm 15 is shaped at its opposite sides in conform ity with the shape of the polar faces that define the air gap. Since the diaphragm 15 is non-magnetic, there is no normal drag on the diaphragm in one direction or the other by the magnetic field.

' Attention is called to the fact that, since all parts of the operative mechanism are mounted on the base 9, they can be secured upon the base and properly adjusted before insertion into the casing. This makes the assembling and final adjustment of the instrument comparatively easy, because the subsequent handling of the .base and the parts carried thereby does notdisturb any previous adjustment. By simply unscrewing the cap or cover 2, all parts are fully exposed for access.

,If desired, the cylindrical body 1 of the I outer casing may be provided with sound outlets 37 for the lateral emission of sound waves produced by the diaphragm in the directions. This not only gives a stronger reproductionfbut also results in a more even distribution of sound throughout the room in which the loudspeaker is located.

In the modification shown in Fig. 3, the

rod sections 24 for adjusting the spring arms- 18 are actuated from outside the casing by means of a knurled knob or thumb piece 38. The screw-threaded ends of the rod sections 24 engage a cylindrical screw-threaded piece 39 provided on its periphery with gear-teeth 40. In other words, the connecting piece 39 is in effect a small toothed wheel or pinion 40. The knob 38 is connected to the outer end of a rod 41. To the inner end of rod 41 is secured a small gear-wheel or pinion 42 arranged to mesh with pinion 40. The rod 41 is supported at one end in the hub' 43 of the casing, and at the other end by a suitable bracket 44 mounted on base 9 or otherwise held in position. By turning the knob 38, the pinion 40 is rotated one way or the other to separate the rod sections 24 or draiv them closer together. The rod sections 24 in Fig. 3, as well as those in Fig. 1, may be regarded as a single rod axially adjustable in length. The screw-threaded engagement between the rod sections 24 and the member 26 or 39 is such that very delicate adjustments of the spring arms 18 are effected by turning member 26 or knob. 38.

In Figs. 4, 5 and 6 I have shown a telephone transmitter embodying my invention ing. The instrument is'mounted on a suitable base 45 to which is secured a casing 46,

as by screws 46'. The casing 46 is shown cylindrical in form, but it may have any other convenient shape. The rear end of casing 46 is closed by a base plate or disk 47, which is removably secured in place by suitable fastening devices, such as screws 47 The disk 47 carries the electro-magnetic operating mechanism. A permanent steel magnet M is secured to the disk 47 by fastening devices 48. Inorder to secure as great a length of magnet as possible, I prefer to shape it as shown in Fig.4, with the pole pieces 49 extending .toward each other to provide an air gap 50 arranged centrally of the casing. In the magnetic air gap- 50 operates a diaphragm 51, which in this instance is approximately square-shaped in order to extend closely from one polar face to the other. The diaphragm 51 is provided with a pair of resilient extensions 52 supported at their outer ends by resilient arms 53. The extensions 52 are preferably corrugated transversely so as to provide the proper degree of resiliency for the diaphragm 51, which should respond instantly and properly to the sound waves projected against it. The diaphragm 51 and its resilient support-- ing extensions 52 constitute a vibratory unit substantially identical with the vibratory unit 1516 previously described in detail.

7 Similarly, the connections between the ex tensions 52 and the spring arms 53 are like the connections between the extensions 16 and the spring arms 18 of Fig. 1. Consequently, in order to avoid needless repetition, itwill be understood that the previous detailed description of the construction and operation of the vibratory unit 1516 and the supporting spring arms 18, shall be considered as fullyapplicable to the vibratory unit 51'52 and the supporting arms 53.

In the construction of Figs. 4, 5 and 6, the resilient supporting arms 53 are adjusted by means of a single rod 54 having opposite screw-threads 55 and 56 near its ends. The rod 54 projects at its ends through elongated openings 57 in the arms 53. On the screwthreads 55 and 56 of rod 54 are mounted cyfreverse direction, the spring arms are forced apart, precisely .as described in connection with the two-part rod 24 in Fig. 1. The

urpose and function of the cylindrical earings 58 are exactly the same as ex-.

plained in reference to the bearings 27 of Fig. 1. Theelongated 0peni ngs57 and 61 in the spring arms 53 and retaining plates 60, respectively, allow for rocking movement of the arms 53 without interfering with the rotation of rod 54.

In order to allowready and easy manipulation of the adjusting rod 54, I connect the same to a suitable finger piece, such as a.

By turning the knob 62 in such a direction.

that the slot. 64 faces directly toward the rear of casing 46, the flat projection 65 of rod 54 will automatically enter this slot when the mechanism is inserted into the casing from the rear. It will be noticed that the entire length of rod 54 is less than the diameter of casing 46, so that the rod does not interfere with the insertion and removal of the entire mechanism into and from the casing.

On the rear face of base plate 47 are mounted suitable terminals or binding posts 67, to which are connected conductors 68 leading from the extensions 52 of the vibratory unit. Circuitdeads 69 are connected to the terminals 6.7 and these leads may conveniently beled out of a hole 7 O in the lower end of the rear cover 71. This cover is preferably mounted on the casing so as to be readily removable therefrom. For instance, the casing 46 may have a series of headed pins or lugs 72 arranged to engage bayonet slots 73 in the cover, as shown in the fragmentary view of Fig. 7. The front cover 74 of the instrument is provided with a sound opening 75 opposite the diaphragm 51. If desired, the opening 75 may be covered wit-h gauze or similar material. The

cover 74 is preferably mounted on the casing so as to be quickly and easily removable to expose the inside mechanism. For this purpose, a separable bayonet slot connection may and 74 may be of identical shape and formed from sheetmetal, fiber, composition material, etc., in the same die or mold, and they may be made as ornamental as desired.

It is self-evident that the various parts of the instrument, other than the magnet itself, should be made of non-magnetic material, so as to prevent the weakening of the magnetic field across the air gap. There would,

be used, as shown in Fig. 7, or any other practlcal connection. The covers 71 advisable to attach around the opening 75- perhaps, be no objection to making the spring arms 53 of magnetic material, because these arms are arranged at right angles to the magnet-and outside the directlon of the magnetic flux. The mere fact that the cross-connection ofthe arms 53 is in contact with the base of the magnet at the center or neutral part thereof, would not cause magnetic leakage through the arms 53, if the instrument is otherwise properly construct ed. The same holds true for the sprmg arms 18 in Fig. 1.

The casing 46 ma be provided with a series of small soun openings 76 to prevent the formation of air cushions back of the diaphragm 51 during the vibrations thereof.

Although I have described the instrument of FigsA, 5 and 6 as a transmitter, it is obvious that the same may be used as a receiver. In that event, it would perhaps be a sound amplifying extension.

In Fig. 9, I have shown, in a diagrammatic way, a modification including)a diaphragm 77 resiliently suspended springs 78 arranged to operate in the air gap formed between the magnetic pole pieces 79 and 80 of a suitable magnet (not shown). Each pair of springs 78 is connected to a bar 81 aiiixed to a square rod 82, which is slidably mounted in a suitable support 83. The

. outer end of each rod 82 is screw-threaded at 84, and on this screw-threaded end is mounted a knob or other finger piece 85 for manual adjustment. By turning the knobs 85 one way or the other, the tension of the springs 78 is regulated, for the purgpse previously described in reference to the 'aphragm in Figs. 1 and 4. The Springs 78 are preferably used as conductors for connecting the non-magnetic diaphragm 77 in the'desired circuit. Otherwise, what has been said about the diaphra s 15 and 51 is applicable to diaphragm 7 It will be clear from the foregoing description of the several embodiments illust'rated in the drawings that I have provided a telephone instrument of simple construction and high efliciency in the electric transmission and reproduction of sound waves. The vibratory acoustic element is selfactuating, in that it requires no separate member to set it in operation. This acoustic element represents a construction of uttermost sim hcity.

The efliclency of the instrument is enhanced by the absence of a pivoted armature which is liable to strike the pole pieces, by the absence of an edge-bound diaphragm with. a fundamental note of its own and con nected to the armature by rods or links in which lost motion is almost unavoidable, and by the absence of an coil that is bound to have a disturbing effect by its self-induction. The parts composing the operative mechanism in my new instrument are so few and may be so compactly arranged that the instrument can be constructed considerably smaller than shown in the drawings. I have purposely exaggerated the proportion of parts in the drawings for the sake of clearness, so that these drawings are not to betaken as actual working drawings.

Although I have herein shown and described certain specific constructions, I want it clearly understood that I have done so 1. In a telephone instrument, a magnet having an air gap, an acoustic diaphragm of rigid non-magnetic conducting material resiliently mounted to vibrate bodily "'1 said air gap, and means for connecting said diaphragm in an electric circuit.

2. In a telephone instrument, a magnet havingan air gap, an acoustic diaphragmof rigid non-magnetic conducting material mounted to vibrate in said air gap in a dimotion at right angles to its own plane, and

means connected to said diaphragm for resiliently supporting the same in said air gap, said diaphragm being adapted to form part of an electric circuit.

3. In a telephone instrument, a magnet having an air gap, an acoustic diaphragm of rigid non-magnetic conducting material mounted to vibrate in said air gap in a direction at right angles to its own plane, and connections at opposite ends of said diaphragms for resiliently supporting) the same in said air gap, said connections eing of conducting material to connect the diaphragm in circuit.

4. In a telephone instrument, a magnet having an air gap," an acoustic diaphragm of non-magnetic conducting material mount ed to vibrate in said air gap in a direction at right angles to its own plane, connections at opposite ends of said diaphragm for resiliently supporting the same in said air gap, said connections being of conducting material to connect the diaphragm in circuit, and means for simultaneously adjusting the degree of resiliency of said connections.

5. In a telephone instrument having a magnetic air gap, an acoustic diaphragm of a non-magnetic conducting plate or disk mounted to yibrate as a rigid body in said air gap and adapted to be connected in cir- 'cuit, resilient extensions integral with said diaphragm for operatively supporting the same in said air gap, and means for adjusting the degree of resiliency of said extensions.

6. In a telephone instrument having a magnetic air gap, a, rigid acoustic diaphragm t non-magnetic conducting material provided with resilient extensions for supporting the diaphragm for vibratory movement in said air gap, said diaphragm being adapted to be connected in an electric circuit and having a width greater than that of said extensions, so that the acoustic area .provided with a base, a frame secured to said base and having a pair of spring arms, and a diaphragm connected to and supported between said arms for vibratory movement, said frame and said diaphragm being attachable to and removable from said base as a unit.

9. In a telephoneinstrument having a magnetic air gap, a pair of supporting spring arms, resilient tension members connected to said arms, an acoustic diaphragm connected at opposite points to said mem-- bers and arranged to vibrate in said air gap, whereby said diaphragm is resiliently suported b and between said members for odily vi ratory movement, and means for slmultaneously adjusting said spring arms to vary the normal tenslon of said resilient members.

10. In a telephone instrument, an acoustic d aphragm in the form of a rigid plate or (118k of sheet metal provided with resilient tenslon members connected to and project- :ing from opposite ends of the diaphragm.

11. telephone instrument having means to provide a magnetic field, a pluralit of resilient tension members, and a rigi edgefree diaphragm of non-ma netic conducting material supported by and etween said tension members for vibratory movement in said field.

12. In a telephone instrument,-a pair of ad ustable arms, a vibratory unit arranged between said arms and connected thereto for support, said .unit being inherently resilient,.

and means for simultaneously adjusting said arnis to vary the normal resiliency of said 13. In a telephone instrument, an edgefree vibratory diaphragm consisting of a rigid plate or disk resiliently supported and electrically self-actuating.

14'. In a telephone instrument, a vibratory diaphragm provided with a pair of integral extensions projecting from opposite edges of the diaphragm for supporting the same, said diaphragm being of greater rigidity than said extensions.

15. In atelephone instrument, axons-piece vibratory unit of metal consisting of a rigid diaphragm and a pair of fiat strips extending integrally from said diaphragm at diametrically opposite points thereof, said strips being transversely corrugated to provide a resilient support for the diaphragm.

16. In a telephone instrument, an acoustic I diaphragm consisting of a rigid plate or disk, and means engaging the edge of said diaphragm at only two points diametrically oplposite for resiliently supporting the diagractically uniform amplitude over'its entire surface.

17. In a telephone instrument, a substantially closed outer casing, a' resilient vibratory unit in said casing, means for maintaing saidunit constantly under tension, and means operable from outside said casing for controlling the normal tension of said unit.

18. In a telephone instrument, a substantially closed outer casing, a magnet in said casing, an acoustic edge-free diaphragm of sheet metal in operative relation to said magnet, a plurality of resilient tension members connected to opposite ends of said diaphragm for resiliently supporting the same for bodily vibratory movement, and means operable from outside said casing ,for adjusting the degree of resiliency of said members.

having a pair of spring arms, and a vibratory unit supported by and between said arms, said unit including a rigid edge-free diaphragm.

20. In a telephone instrument, a frame having a pair of spring arms, a resilient vibratory unit supported by and between said arms, and manually adjustable means for simultaneously moving said arms to vary the distance between the supporting ends of said arms and thereby controlling the resiliency of said vibratory unit.

21. In a telephone instrument, a frame having a pair of spring arms, a resilient vibratory unit supporte by and between said arms, a manually adjustable rod engaging said arms to force them apart or bring themtoward each other, and means included in the connections between said arms and said rod for automatically compensating for the rocking movements of said arms.

92. In an' electric instrument, a base, a

ragm to permit vibratlon thereof with 19. In a telephone instrument, a frame substantially U-shaped magnet mounted on said'base, a substantially U-shap'ed, frame mounted on said base at approximately right angles to said nfa et, and a vibratory unit supported by sai frame in operative relation to said magnet.

23. In a telephone instrument, a frame having a pair of spring arms, a vibratory unit sup orted by and between said arms, a rotary ger piece, and connecting means between said finger piece and said arms for simultaneously moving said arms toward or away from each other. I

24. In a telephone instrument, a substantially closed outer casingfa resilient vibratory unit in said casing, means for maintaining said unit constantly under tension,

a rotary finger piece outside said casingfand connections'between said finger 'iece and said tensioning means to control t e degree 

